U.S. patent number 7,719,184 [Application Number 11/460,818] was granted by the patent office on 2010-05-18 for organic el element having a protective layer.
This patent grant is currently assigned to Kyocera Corporation. Invention is credited to Hiromi Fukuoka, Taro Hasumi, Keigo Kanoh, Mitsuo Morooka, Masaya Watanabe.
United States Patent |
7,719,184 |
Kanoh , et al. |
May 18, 2010 |
Organic EL element having a protective layer
Abstract
Provided is an organic EL element including: a first electrode
13; a protection layer 15 that is formed on the first electrode 13
and has an opening portion through which the first electrode 13 is
exposed; an insulation layer 17 that is formed on the protection
layer 15; an organic layer 19 that is formed over the insulation
layer 17 and the first electrode 13 exposed through the opening
portion, and includes an emission layer; and a second electrode 21
formed on the organic layer 19, wherein a film thickness of the
protection layer 15 is less than that of the organic layer 19.
Inventors: |
Kanoh; Keigo (Yamato,
JP), Morooka; Mitsuo (Kawasaki, JP),
Hasumi; Taro (Yamato, JP), Fukuoka; Hiromi
(Yamato, JP), Watanabe; Masaya (Yamato,
JP) |
Assignee: |
Kyocera Corporation (Kyoto,
JP)
|
Family
ID: |
38080647 |
Appl.
No.: |
11/460,818 |
Filed: |
July 28, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070176545 A1 |
Aug 2, 2007 |
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Foreign Application Priority Data
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Jul 29, 2005 [JP] |
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2005-220976 |
May 29, 2006 [JP] |
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2006-148927 |
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Current U.S.
Class: |
313/506; 428/917;
428/690; 313/504; 313/503; 257/40 |
Current CPC
Class: |
H01L
27/3246 (20130101); Y10S 428/917 (20130101); H01L
2251/5315 (20130101) |
Current International
Class: |
H05B
33/00 (20060101); H05B 33/06 (20060101) |
Field of
Search: |
;313/504-506
;428/690,917 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2001-185363 |
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Jul 2001 |
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JP |
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2004-296297 |
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Oct 2004 |
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JP |
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Primary Examiner: Roy; Sikha
Attorney, Agent or Firm: Hogan & Hartson LLP
Claims
What is claimed is:
1. An organic EL element comprising: a first electrode; a
protection layer that is formed on the first electrode and has a
first opening portion through which the first electrode is exposed;
an insulation layer formed on the protection layer and having a
second opening portion and an upper surface around an opening of
the second opening portion, the second opening portion being formed
in a region corresponding to the first opening portion of the
protection layer; an organic layer that is formed on lateral sides
of the first opening portion and the second opening portion, the
upper surface of the insulation layer, and the first electrode
exposed through the first opening portion, and includes an emission
layer; and a second electrode formed on the organic layer, wherein
a film thickness of the protection layer is less than that of the
organic layer.
2. The organic EL element according to claim 1, wherein the film
thickness of the protection layer is less than that of the second
electrode.
3. The organic EL element according to claim 1, wherein a film
thickness of the insulation layer is tapered toward the second
opening portion.
4. The organic EL element according to claim 1, wherein the lateral
side of the first opening portion of the protection layer is
deviated to outside the lateral side of the second opening portion
of the insulation layer, and the deviation width is no more than 1
.mu.m.
5. The organic EL element according to claim 1, wherein the first
electrode is formed of aluminum, an aluminum alloy, silver, or a
silver alloy, and the protection layer is formed of molybdenum.
6. An organic EL element comprising: a first electrode; a
protection layer formed on the first electrode and having a concave
portion; an insulation layer formed on the protection layer and
having an opening portion and an upper surface around an opening of
the opening portion, the opening portion being formed in a region
corresponding to the concave portion of the protection layer; an
organic layer that is formed on lateral sides of the concave
portion and the opening portion of the insulation layer, the upper
surface of the insulation layer, and the protection layer exposed
through the opening portion of the insulation layer, and includes
an emission layer; and a second electrode formed on the organic
layer, wherein a depth of the concave portion is less than a film
thickness of the organic layer.
7. The organic EL element according to claim 6, wherein the depth
of the concave portion of the protection layer is less than the
film thickness of the second electrode.
8. The organic EL element according to claim 6, wherein the lateral
side of the concave portion of the protection layer is further
deviated outside the lateral side of the opening portion of the
insulation layer, and the deviation width is no more than 1
.mu.m.
9. The organic EL element according to claim 6, wherein a film
thickness of the insulation layer is tapered toward the opening
portion.
10. The organic EL element according to claim 6, wherein the first
electrode is formed of aluminum, an aluminum alloy, silver, or a
silver alloy, and the protection layer is formed of molybdenum.
11. An organic EL element comprising: a first electrode; a
protection layer formed on the first electrode and having a concave
portion; an insulation layer formed on the protection layer and
having an opening portion through which the protection layer is
exposed; an organic layer that is formed over the insulation layer
and the protection layer exposed through the opening portion of the
insulation layer, and includes an emission layer; and a second
electrode formed on the organic layer, wherein a depth of the
concave portion is less than a film thickness of the organic layer,
and the protection layer in a region where the concave portion is
formed has a thickness of not more than 10 nm.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. .sctn.119
to Japanese Patent Application No. 2005-220976, filed Jul. 29, 2005
and Japanese Patent Application No. 2006-148927, filed May 29,
2006. The contents of this application are incorporated herein by
reference in their entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an organic EL element.
2. Description of the Related Art
In an organic electroluminescence (EL) element, an electric field
is applied to an organic fluorescent compound so as to be excited
to emit light. Characteristics of the organic EL element include
self-illumination, a wide viewing angle, a high response speed, a
low driving voltage, and full color. The organic EL element has
currently been put to practical use, and may apply to a flat color
display device such as a compact display panel, an out-door screen,
or a screen for a personal computer or a television set.
The organic EL element has a structure in which an organic layer
having a luminescence characteristic is interposed between two
electrodes. When a DC voltage is applied to the two electrodes, a
hole is injected from a positive electrode to the organic layer,
and an electron is injected from a negative electrode to the
organic layer. According to the electric field generated in
response to the applied voltage, these carriers are transferred
inside an organic emission layer, and thereby carrier recombination
occurs.
A part of energy emitted when the electron and the hole are
recombined is used to excite a luminescent molecule. When the
excited luminescent molecule emits energy and thus returns to a
ground state, a certain portion of the energy is emitted in the
form of a photon. This is an emission principle of the organic EL
element.
When manufacturing the organic EL element, a driving element such
as a TFT, which is used to drive the organic EL element, a
conductive pattern and the like are formed on a substrate (i.e., a
glass substrate), and then they are covered by a flattening film.
Thereafter, a first electrode, an insulation layer, an emission
layer, and a second electrode are formed in this order on the
flattening film.
However, while the first electrode is subjected to the above
processes, process damage may occur, or dust may be attached onto
the first electrode. This affects to a characteristic of the
organic EL element, which leads to deterioration in emission
quality.
To cope with the above problem, a technique has been proposed in
which the organic EL element is produced by sequentially laminating
a first electrode, a protection film, an emission layer composed of
an organic material, and a second electrode on a substrate, and by
removing the protection film existing in a pixel area on the first
electrode before the emission layer is laminated (Japanese
Unexamined Patent Publication No. 2001-185363). According to this
technique, the protection film has a film thickness of 1 .mu.m, and
the organic layer has a film thickness of 1,250 .ANG., where the
film thickness of the protection film is greater than that of the
organic layer.
SUMMARY OF THE INVENTION
According to an aspect of the present invention, there is provided
an organic EL element comprising: a first electrode; a protection
layer that is formed on the first electrode and has a first opening
portion through which the first electrode is exposed; an insulation
layer formed on the protection layer and having a second opening
portion in a region corresponding to the first opening portion of
the protection layer; an organic layer that is formed over the
insulation layer and the first electrode exposed through the first
opening portion, and includes an emission layer; and a second
electrode formed on the organic layer. In this case, a film
thickness of the protection layer is less than that of the organic
layer.
According to another aspect of the present invention, there is
provided an organic EL element comprising: a first electrode; a
protection layer formed on the first electrode and having a concave
portion; an insulation layer formed on the protection layer and
having an opening portion through which the protection layer is
exposed; an organic layer that is formed over the insulation layer
and the protection layer through which the opening portion of the
insulation layer, and includes an emission layer; and a second
electrode formed on the organic layer. In this case, a depth of the
concave portion is less than a film thickness of the organic
layer.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other features and advantages of the present
invention will become more apparent by describing in detail
exemplary embodiments thereof with reference to the attached
drawings in which:
FIG. 1 is a cross-sectional view showing a structure of an organic
EL element according to a first embodiment of the present
invention;
FIGS. 2 to 6, 7A, and 7B are cross-sectional views explaining a
manufacturing method of an organic EL element according to the
first embodiment of the present invention;
FIGS. 7C, 7D and 7E are cross-sectional views explaining a
manufacturing method of a known organic EL element;
FIGS. 8 and 9 are cross-sectional views explaining a manufacturing
method of an organic EL element according to the first embodiment
of the present invention; and
FIG. 10 is a cross-sectional view showing a structure of an organic
EL element according to a second embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an organic EL element and a manufacturing method
thereof according to exemplary embodiments of the present invention
will be described in detail with reference to the accompanying
drawings. The present invention is not limited to the following
descriptions, but various changes may be made therein without
departing from the gist of the invention. To facilitate
understanding, each element may be shown in a different scale from
its actual scale.
First Embodiment
FIG. 1 is a cross-sectional view showing a schematic structure of
an organic EL element according to a first embodiment of the
present invention. As illustrated in FIG. 1, the organic EL element
includes a substrate portion 11 and an organic electroluminescence
element portion 12 on the substrate portion 11. The substrate
portion 11 includes a substrate such as a glass substrate, a
driving element such as a TFT used to drive the organic
electroluminescence element portion 12, a conductive pattern, and a
flattening layer which covers the driving element and the
conductive pattern. The organic EL element employs a top emission
type structure in which light is obtained from a top surface side
of the organic electroluminescence element portion 12.
As illustrated in FIG. 1, the organic electroluminescence element
portion 12 includes a lower electrode (anode electrode) 13 that is
a first electrode formed on the substrate portion 11, a protection
layer 15 that is formed on the lower electrode 13. The protection
layer 15 has an opening portion where a part of the lower electrode
13 is exposed from the protection layer 15. The organic
electroluminescence element portion 12 further includes, a
interlayer-insulation layer 17 that is formed on the protection
layer 15, an organic electroluminescence layer (organic layer) 19
that is formed on the exposed region of the lower electrode 13 and
the interlayer-insulation layer 17, and an upper electrode (cathode
electrode) 21 that is a second electrode formed on the organic
electroluminescence layer.
The lower electrode (anode electrode) 13 is formed of a material
having a high light reflectance such as aluminum (Al) or its alloy,
an alloy of aluminum (Al) and neodymium (Nd), an alloy of aluminum
(Al) and yttrium (Y), or silver (Ag) or its alloy. Since the lower
electrode 13 is formed of the material having a high light
reflectance, light acquisition efficiency can be enhanced in the
top emission type organic EL element, and light emitted from the
organic electroluminescence layer 19 can be effectively
utilized.
In the process of manufacturing the organic electroluminescence
element portion 12, which will be described below, the protection
layer 1S protects the lower electrode 13 from process damage after
the lower electrode 13 is formed until the organic
electroluminescence layer 19 is formed.
In this case, the protection layer 15 is required to be formed of a
material by which etching can be selectively performed by using
wet-etching. Further, in the process of forming the
interlayer-insulation layer 17 as to be described below, the
protection layer 15 is preferably formed of a durable material
capable of protecting the lower electrode 13 from the process
damage. That is, the protection layer 15 is preferably formed of a
material that is durable against a developing solution used to
pattern the interlayer-insulation layer 17.
Preferably, the protection layer 15 has a good adherence property
with respect to the lower electrode 13. Thus, a problem caused when
the protection layer 15 is peeled off can be prevented
satisfactorily. For example, the material that meets the
requirement for the protection layer 15 may be molybdenum (Mo) or
its alloy.
Since the protection layer 15 is formed of molybdenum (Mo) or its
alloy, when the lower electrode 13 is formed of aluminum or its
alloy, the protection layer 15 can have a good adherence property
with respect to the lower electrode 13. Accordingly, a problem
caused when the protection layer 15 is peeled off can be prevented
satisfactorily.
The material forming the protection layer 15 is not limited to a
metal material. Thus, an insulation material such as silicon
nitride may be used.
The organic electroluminescence layer 19 includes an emission layer
that uses an organic material as an emission material. The organic
electroluminescence layer 19 may employ either a single layer
structure or a multilayer structure in which layers are laminated
based on functions. For example, in the case of single layer
structure in which the organic electroluminescence layer 19 is
formed to be a single layer having only the emission layer, the
emission layer may be formed of a host material in which a dopant
material having a luminescent characteristic is doped, having a
hole transport characteristic and an electron transport
characteristic. Also, the emission layer may be formed of a
material having a hole transport characteristic, an electron
transport characteristic and a luminescent characteristic. With
this single layer structure, the process of forming element can be
simplified. In addition, the organic EL element can be produced at
a low price.
On the other hand, for example, when the organic
electroluminescence layer 19 employs the multilayer structure, the
organic electroluminescence layer 19 comprising the emission layer
further comprises a single layer or a plurality of layers selected
from among a hole transport layer, a hole injection layer, a hole
blocking layer, an electron transport layer, an electron injection
layer, and an electron blocking layer. For example, in the case of
multilayer structure in which the organic electroluminescence layer
19 is composed of the emission layer, the hole blocking layer and
the electron transport layer, the hole blocking layer is formed
between the lower electrode 13 functioning as an hole injection
electrode and the electron transport layer, in order to control the
amount of charge carriers injected from the lower electrode 13 and
the upper electrode 21 and to have the substantially same density
of both the hole and the electron in a portion where they are
recombined. With this structure, emission efficiency can be
improved. In the case of multilayer structure in which the organic
electroluminescence layer 19 is composed of the emission layer, the
electron blocking layer and the hole transport layer, the electron
blocking layer may be formed between the upper electrode 21
functioning as an electron injection electrode and the hole
transport layer.
In order to obtain light from the top surface side of the organic
electroluminescence element portion 12, the upper electrode 21 is
formed of a transparent conductive material such as indium tin
oxide (ITO) or tin oxide.
In the organic EL element having the aforementioned structure
according to the present embodiment, the protection layer 15 has a
film thickness less than that of the organic electroluminescence
layer 19. Thus, the disruption of the organic electroluminescence
layer 19 caused by a step difference at the opening portion of the
protection layer 15 can be effectively prevented. As a result, the
lower electrode 13 is prevented from being exposed through a
disrupted portion of the organic electroluminescence layer 19.
Further, the upper electrode 21 and the lower electrode 13 are
prevented from short-circuiting through the disrupted portion in a
satisfactory manner.
In addition, in the organic EL element having the aforementioned
structure according to the present embodiment, the protection layer
15 has a film thickness less than that of the upper electrode 21.
Thus, the upper electrode 21 is prevented from disconnection caused
by the step difference at the opening portion of the protection
layer 15. Further, the upper electrode 21 is effectively prevented
from poor conductivity caused thereby.
In the organic EL element having the aforementioned structure
according to the present embodiment, the protection layer 15 may
have a film thickness of about 5 nm to 500 nm, preferably, about 5
nm to 100 nm. In terms of preventing disruption of the organic
electroluminescence layer 19 or disconnection of the upper
electrode 21, a thickness of the interlayer-insulation layer 17
does not matter so much for the following reasons. That is, since a
film thickness of the interlayer-insulation layer 17 is thin near
the opening portion of the protection layer 15, and a surface of
the interlayer-insulation layer 17 near the opening portion has a
relatively gentle slope, the organic electroluminescence layer 19
or the upper electrode 21 is satisfactorily attached to this
portion. Therefore, the thickness of the interlayer-insulation
layer 17 does not matter so much.
Further, in the organic EL element having the aforementioned
structure according to the present embodiment, the protection layer
15 is located such that a lateral side of the opening portion
thereof is deviated to outside a lateral side of the
interlayer-insulation layer 17. In this case, an indentation at the
lateral side of the opening portion of the protection layer 15 is
formed. In this indentation, the amount of positional deviation
between the lateral side of the opening portion and the lateral
side of the interlayer-insulation layer 17 is determined to be 1
.mu.m or less. Accordingly, the disruption of the organic
electroluminescence layer 19 and the disconnection of the upper
electrode (cathode electrode) 21 which are caused by the
indentation formed near the opening portion of the protection layer
15 are effectively prevented. Further, poor conductivity caused
thereby can be effectively prevented. When the amount of positional
deviation is no more than 1 .mu.m, the organic electroluminescence
layer 19 and the upper electrode 21 become easy to fill in the
indentation near the opening portion of the protection layer 15.
Thus, the organic electroluminescence layer 19 and the upper
electrode 21 can be restricted from peeling off around the
indentation. Moreover, since the interlayer-insulation layer 17
near the opening portion is satisfactorily supported by the organic
electroluminescence layer 19 and the upper electrode 21 in the
indentation, shape deformation of the interlayer-insulation layer
17 can be effectively avoided.
Accordingly, in the organic EL element according to the present
embodiment, quality deterioration caused by process damage during
manufacturing can be avoided by the protection layer 15. Further,
the disruption of the organic electroluminescence layer 19 and the
disconnection of the upper electrode 21 which are caused by the
step difference and the indentation of the protection layer 15 can
be effectively avoided. Furthermore, poor conductivity of the upper
electrode 21 caused thereby can be effectively avoided, realizing a
high quality organic EL element.
A driving method of the present invention may be either a passive
matrix method or an active matrix method. In addition, a structure
of the present invention may be a bottom emission type structure in
which light is obtained through the substrate portion.
Now, a manufacturing method of the organic EL element according to
the above-mentioned embodiment will be described with reference to
the accompanying drawings.
First, the substrate (i.e., a glass substrate) is prepared, and the
driving element such as a switching TFT, the conductive pattern and
the like are formed on the substrate, and then a flattening
insulation layer covers the driving element, the conductive pattern
and the like, thereby the substrate portion 11 illustrated in FIG.
2 is formed.
Next, as illustrated in FIG. 3, for example, aluminum (Al) film as
the lower electrode 13 is formed on the substrate portion 11.
Subsequently, as illustrated in FIG. 4, for example, a molybdenum
(Mo) film as a protection-material layer 15a is formed on the lower
electrode 13. In this process, a film thickness of the
protection-material layer 15a is less than that of the upper
electrode 21 which is to be formed later.
As a result, disruption of the organic electroluminescence layer 19
formed in a later process, disconnection of the upper electrode 21,
and poor conductivity of the upper electrode 21 can be effectively
prevented when side etching of the protection-material layer 15a
takes place in the etching process of the protection-material layer
15a. Further, the film thickness of the protection-material layer
15a is preferably 5 nm to 500 nm, more preferably 5 nm to 100
nm.
Since the lower electrode 13 and the protection-material layer 15a
are formed by combining aluminum (Al) and molybdenum (Mo), the
lower electrode 13 can have a good adhesive property with respect
to the protection-material layer 15a, and a problem caused when the
protection-material layer 15a is peeled off can be effectively
prevented. With this combination, the protection-material layer 15a
can be formed in a sputtering method by only replacing a chamber
after the lower electrode 13 is formed in the sputtering method.
Thus, the lower electrode 13 and the protection-material layer 15a
can be effectively formed.
Next, as illustrated in FIG. 5, an insulation material layer 17a is
formed on the protection-material layer 15a. Then, the insulation
material layer 17a is patterned in etching by using the
protection-material layer 15a as a stopper, and as illustrated in
FIG. 6, the interlayer-insulation layer 17 having an opening
portion corresponding to a pixel area is formed on the
protection-material layer 15a. That is, the opening portion is
formed by partially removing the insulation material layer 17a
using a general photolithography technique, thereby obtaining the
pixel area. In this case, the interlayer-insulation layer 17 is
patterned such that its film thickness decreases near the opening
portion. In order for the interlayer-insulation layer 17 to have
this structure, positive resist material (i.e. acrylate resin) may
be used as material of the insulation material layer 17a. When the
insulation material layer 17a formed of the positive resist
material is irradiated by light, and an irradiated portion is
removed, thereby the opening portion of the insulation material
layer 17a is formed. However, since light hardly reaches a lower
side (the substrate portion 11 side) of the insulation material
layer 17, the opening portion of the insulation material layer has
an opening area narrower at its lower side than its upper side. As
a result, a thickness of the interlayer-insulation layer 17 is
gradually decreased near the opening portion.
Due to a low durability against a developing solution (an etchant)
used to remove the insulation material layer 17a, the lower
electrode 13 formed of aluminum (Al) or its alloy is dissolved in
the developing solution. However, in the present embodiment, the
protection-material layer 15a that is durable against the
developing solution is formed on the lower electrode 13.
Accordingly, the lower electrode 13 is scarcely dissolved in the
developing solution even in the process of removing the insulation
material layer 17a, and a surface of the lower electrode 13 is
restrained from becoming rough. Therefore, even after the process
of the removing the insulation material layer 17a, the surface of
the lower electrode 13 can maintain to be satisfactorily flattened
as much as when the lower electrode 13 is formed. Further,
darkening can be effectively prevented when an electrical short
occurs between electrodes.
Although the protection-material layer 15a is removed in the
following process, since the protection-material layer 15a covers
over the lower electrode 13 until before the organic
electroluminescence layer 19 is formed, the lower electrode 13 can
be prevented from deterioration in its characteristic caused by an
oxide film formed on its surface.
Subsequently, as illustrated in FIG. 7A, a lower side of the pixel
area, that is, the protection-material layer 15a at the lower side
of the opening portion, is selectively removed in wet-etching by
using the interlayer-insulation layer 17 as a mask, and an opening
portion is formed in the protection-material layer 15a by exposing
the surface of the lower electrode 13, thereby forming the
protection layer 15. It is desirable that an etchant used to remove
the protection-material layer 15a in selective etching has a
selection ratio greater than 10. By using the etchant having its
selection ratio greater than 10, the protection-material layer 15a
can be selectively removed at only a desirable portion without
nearly deforming shapes of the interlayer-insulation layer 17 and
the lower electrode (anode electrode) 13.
An etchant having its selection ratio in the range of 20 to 30 is
more preferably used. By using the etchant, the protection-material
layer 15a can be further satisfactorily removed at only a desirable
portion. For example, as for the etchant that is used for
selectively etching the protection-material layer 15a formed of
molybdenum (Mo), a mixed acid may be used which contains nitric
acid of 15 wt %.about.35 wt %, acetic acid of 25 wt %.about.45 wt
%, and phosphoric acid of 0.1 wt %.about.5 wt %. Such a mixed acid
may be CMK123 (nitric acid:acetic acid:phosphoric
acid=26:36:2).
As illustrated in FIG. 7B, the protection layer 15 formed by
selectively removing the protection-material layer 15a has a side
etching width W1 of 1 .mu.m or less. The side etching width W1 can
be adjusted by selecting a film thickness of the
protection-material layer 15a or by selecting an etchant. For
example, when the aforementioned CMK123 is used as the etchant, the
side etching width W1 can be 1 .mu.m or less by performing
wet-etching in a shower manner, a dip manner, or a paddle manner
for an etching time of 10 to 30 seconds. By allowing the side
etching width W1 to be 1 .mu.m or less, the disruption of the
organic electroluminescence layer 19 and the disconnection of the
upper electrode 21 which are caused by the indentation of the
protection layer 15 formed by the side etching can be effectively
prevented, and poor conductivity of the upper electrode 21 caused
thereby can be effectively prevented. Further, when the side
etching width W1 is 1 .mu.m or less, the organic
electroluminescence layer 19 and the upper electrode 21 become easy
to fill in the indentation near the opening portion of the
protection layer 15. Thus, the organic electroluminescence layer 19
and the upper electrode 21 can be restricted from peeling off
around the indentation. Furthermore, shape deformation of the
interlayer-insulation layer 17 which is caused by the indentation
can be effectively avoided.
In the case that the film thickness of the protection layer 15 is
greater than that of the organic electroluminescence layer 19 or
the upper electrode 21 to be formed later, if a step coverage is
not sufficient when the organic electroluminescence layer 19 or the
upper electrode 21 is formed, it becomes easy for the organic
electroluminescence layer 19 or the upper electrode 21 to be
disrupted at the lateral side of the opening portion of the
protection layer 15. On the other hand, as illustrated in FIG. 7C,
if a side etching width W2 of the protection layer 15 is
significantly wider than as in the case of FIG. 7B, the organic
electroluminescence layer 19 cannot filled in the indentation of
the protection layer 15 formed by the side etching. Thus, a support
for supporting the organic electroluminescence layer 19 is not
present near the indentation. As a result, as illustrated in FIG.
7D, the organic electroluminescence layer 19 is easy to be
disrupted into an organic electroluminescence layer 19a, an organic
electroluminescence layer 19b, and an organic electroluminescence
layer 19c due to the indentation thereof.
On the other hand, as illustrated in FIG. 7E, even if the organic
electroluminescence layer 19 is not disrupted, the organic
electroluminescence layer 19 does not enter into the indentation of
the protection layer 15 formed by the side etching and a void in
the indentation is formed. Thus, the organic electroluminescence
layer 19 becomes easy to be peeled off around the void. Further,
when stress between the organic electroluminescence layer 19
disposed at the upper side of the interlayer-insulation layer 17
and the protection layer 15 disposed at the lower side of the
interlayer-insulation layer 17 is unbalanced due to the void, the
interlayer-insulation layer 17 may deform its shape.
However, in the present embodiment, the side etching width W1 can
be 1 .mu.m or less by selectively removing the protection-material
layer 15a as illustrated in FIG. 7B, thereby satisfactorily
preventing such a problem.
Next, as illustrated in FIG. 8, the organic electroluminescence
layer 19 is formed on the lower electrode 13 and the
interlayer-insulation layer 17. In this case, the film thickness of
the organic electroluminescence layer 19 has to be greater than
that of the protection layer 15. When the film thickness of the
organic electroluminescence layer 19 is greater than that of the
protection layer 15, even if a step coverage of the organic
electroluminescence layer 19 is poor, the organic
electroluminescence layer 19 can be effectively prevented from
disruption at the lateral side of the opening portion of the
protection layer 15. Further, when the indentation of the
protection layer 15 is filled with the organic electroluminescence
layer 19, the peeling off of the organic electroluminescence layer
19 and the shape deformation of the interlayer-insulation layer 17
which are caused by the indentation can be effectively
prevented.
As illustrated in FIG. 9, the upper electrode 21 is formed on the
organic electroluminescence layer 19. In this case, the film
thickness of the upper electrode 21 has to be greater than that of
the protection layer 15. When the film thickness of the upper
electrode 21 is greater than that of the protection layer 15, even
if a step coverage of the upper electrode 21 is poor, the upper
electrode 21 can be effectively prevented from disruption at the
lateral side of the opening portion of the protection layer 15.
Further, even when the film thickness of the organic
electroluminescence layer 19 is relatively thin, the indentation of
the protection layer 15 is filled with the organic
electroluminescence layer 19. As a result, the peeling off of the
upper electrode 21 and the shape deformation of the
interlayer-insulation layer 17 which are caused by the indentation
can be effectively prevented.
Accordingly, the high quality organic EL element of FIG. 1 can be
achieved in which deterioration in quality of the organic EL
element that occurs when process damage takes place in an electrode
during manufacturing, and poor conductivity of the electrode can be
prevented by forming a new protection layer.
Although the upper electrode 21 and the lower electrode 13 are used
as a cathode electrode and the anode electrode, respectively, in
the aforementioned embodiment, the upper electrode 21 and the lower
electrode 13 may be used as an anode electrode and a cathode
electrode, respectively.
Second Embodiment
FIG. 10 is a cross-sectional view showing a structure of the
organic EL element according to a second embodiment of the present
invention. The following description will focus on a different
structure from the organic EL element according to the first
embodiment of the present invention, and the rest of common
structures will be basically omitted.
Unlike the first embodiment, in the second embodiment, the
protection-material layer 15a existing within the opening portion
of the interlayer-insulation layer 17 is not entirely removed,
instead thereof, the protection-material layer 15a existing within
the opening portion of the interlayer-insulation layer 17 remains
so as to form a concave portion 15b in the protection layer 15. As
a result, the film thickness of the protection layer 15 within an
inner area of the opening portion of the interlayer-insulation
layer 17 is less than that of the protection layer 15 outside the
opening portion of the interlayer-insulation layer 17.
With this structure, the protection layer 15 remains on the lower
substrate 13 within the opening portion. Thus, there is an
advantage in that the lower substrate 13 has less damage than in
the first embodiment when the protection-material layer 15a is
etched.
If the film thickness of the protection layer 15 is great in an
area where the concave portion 15b is formed, light reflectance
tends to decrease at the lower electrode 13 when the organic EL
element employs the top emission type. Thus, it is preferable that
the film thickness of the protection layer 15 is set to 10 nm or
less in the area where the concave portion 15b is formed.
Since a depth d of the concave portion 15b of the protection layer
15 is set to be less than the film thickness of the organic
electroluminescence layer 19, the organic electroluminescence layer
19 can be effectively prevented from disruption caused by the step
difference of the concave portion 15b of the protection layer
15.
Further, since the depth d of the concave portion 15b of the
protection layer 15 is set to be less than the film thickness of
the upper electrode 21, the upper electrode 21 can be effectively
prevented from the disconnection caused by the step difference at a
lateral side of the concave portion 15b of the protection layer 15.
In addition, poor conductive of the upper electrode 21 can be
effectively prevented.
Furthermore, since the lateral side of the concave portion 15b of
the protection layer 15 is deviated to outside the lateral side of
the insulation layer 17, and its positional deviation width is no
more than 1 .mu.m, the organic electroluminescence layer 19 can be
effectively prevented from peeling off caused by a void which is
generated when the organic electroluminescence layer 19 does not to
enter into the indentation of the protection layer 15 formed by the
side etching.
The organic EL element of the present invention is particularly
useful for a color flat display device requiring high quality such
as a display panel, an out-door screen, or a screen for a personal
computer or a television set.
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